1. Field of the Invention
The present invention relates to a method and an apparatus for electrically processing vacuum pressure information.
2. Description of the Related Art
Heretofore, pressure switches for either negative pressure or positive pressure have widely been employed in a pneumatic apparatus or the like.
A description will now be made of one example illustrative of a pressure switch for the negative pressure, which is actuated to convert a pressure value into a pressure signal/electric signal. Such a pressure switch is employed in a negative pressure (vacuum) system including pressurized air, a fluid passage or path and a pneumatic apparatus. That is, the pressure switch is used to confirm whether a subject or object (work) to be fed has been attracted by or released from a suction cup or pad.
FIG. 1 is an exemplary view for describing the manner in which this type of pressure switch has been actuated. A detecting circuit comprising a pressure switch having a carrier diffusion type semiconductor pressure sensor therein, an amplifier, an output circuit and a variable resistor or the like, generates output signals Sa, Sb corresponding to differential pressures A and B relative to preset pressure values at the time of the attraction of the work by the suction pad and the release (vacuum break) of the work from the suction pad. Incidentally, the differential pressures A and B have been set up to avoid undesired chattering action.
The output signal Sb is produced based on a threshold value P.sub.h1 of a relatively high vacuum level. In addition, the output signal Sa is of a signal based on a threshold value P.sub.h2 of a vacuum level lower than P.sub.h1. The output signals Sa, Sb are supplied to a sequence controller operable with a computer for Factory Automation or the like so as to activate various control driving means or the like.
In the above prior art, however, a vacuum displaying means is not normally disposed. Therefore, the attraction of the work by the suction pad and the release of the work from the suction pad are repeated to determine the threshold values P.sub.h1, P.sub.h2. In order to produce the output signals Sa, Sb corresponding to the threshold values P.sub.h1, P.sub.h2, respectively, a variable resistor or the like is used to set up and adjust corresponding pressure. Thus, when a number of pressure switches are disposed in the pneumatic apparatus or the like, there is produced an error between each of pressure values detected from the switches and a preset value, thus creating a difficulty in quantitatively setting up the pressure. Further, the pressure is set up and adjusted in analog form, thereby causing a problem in that it is difficult to accurately set up the pressure. The maximum achievable vacuum level produced by repeatedly attracting the work with the suction pad and releasing the same therefrom varies with the elapse of time. In addition, the number of times (attraction/non-attraction state M shown in FIG. 1) in which the work cannot be subjected to sufficient attraction vacuum level, greatly increases due to malfunctions or undesired changes such as clogging of a filter, deterioration in performance of a vacuum pump or an ejector, leakage of vacuum pressure from a pipe, a joint and a suction pad, difference in type among works, a change in the surface of a work, a change in placement position of a work, fatigue and abrasion of the suction pad, failures of a feed valve, a destruction or burst valve, a vacuum safety valve and a vacuum relief valve at the time of the attraction/non-attraction of the work, etc. It is therefore necessary to subject each of switch output signals (pulse waveform signals) to a latch signal process or the like when a comparison process is made between the output signals Sa in order to previously provide information about the replacement of parts such as a typical filter with new ones. In addition, an apparatus including a signal processing circuit for performing its latch signal process becomes large in size. Thus, pressure switches for the positive pressure also have various drawbacks due to inconvenience similar to those of the pressure switches for the negative pressure.